This application claims the priority of 198 34 137.7-26, filed Jul. 29, 1998, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a method for setting a specific torque in an internal combustion engine.
In order to achieve a specific motor vehicle driving performance desired, for example, by the driver or set by an electronic motor controller, a very quick and precise establishment of a specific set starting torque (set torque) of an internal combustion engine of the vehicle is necessary. To set the desired torque, first a rate of air flow or mass of air is usually determined which has to be delivered to the internal combustion engine in order to achieve the desired set torque. For a throttle valve situated in an air induction tract, by which the air mass fed to the internal combustion engine can be adjusted, a throttle valve angle is determined from the air mass value and is set at the throttle valve by an appropriate adjusting device.
Because flow processes are involved in the feed of air and fuel to combustion chambers in an internal combustion engine, the term "mass" is used herein to always mean a mass flow, i.e., a mass per unit time. In particular, internal combustion engines which operate by the Otto principle are usually fed air, i.e., the amount of fuel fed for combustion is governed by the amount of air fed for combustion. For this purpose such an internal combustion engine has an air mass sensor by which the air mass fed for combustion is measured in order to feed the internal combustion engine an amount of fuel adapted thereto, for example by a fuel injection system.
The determination of a throttle valve angle from an air mass is usually performed through association with a performance graph, in accordance with, for example, the rotary speed of the internal combustion engine. This association of a torque with an air mass and of an air mass with a throttle valve angle is referred to as a control tract.
As especially the actual conditions in which the internal combustion engine chambers operates are different from the marginal conditions under which such performance graphs were recorded during testing, the air mass actually fed to the combustion chambers often differs from the air mass needed in order to achieve the desired set torque, so that the actual torque differs from the required set torque. To remedy this situation, various control processes are known in which a comparison of the set torque and actual torque is performed. On the basis of the difference thus determined between the set air mass and the actual air mass the throttle valve angle is then adjusted. This comparison followed by adjustment is continued in the sense of a regulation until the actual air mass is the same as the set air mass.
DE 43 15 885 C1 describes a method for torque adjustment in which, based on a set torque, a mass stream set value for the air to be delivered to the combustion chambers and the actual measured value is adjusted to the particular set value by adjusting the throttle valve opening angle. The particular set value is determined by an air mass sensor which is located upstream from a throttle valve in an air induction tube of the internal combustion engine.
The operation of a motor vehicle must, as a rule, be adapted to constantly changing marginal conditions; especially, new values must constantly be set for another necessary set torque. Thus, the need for control to make the actual air mass equal to the set air mass is very great, and therefore an intensive regulation of the throttle valve angle usually is performed constantly. Consequently, very great stress is applied to the throttle valve and the corresponding throttle valve adjusting device. Furthermore, the adjustment of the desired set air mass takes time, and regularly so much time that the desired set air mass changes again between times. Therefore, the throttle valve angle change regularly lags behind the desired set air mass.
Furthermore, the adjustment of a desired set torque depends primarily on the correctness of the reading of the actual air mass. The air mass sensors usually used in determining the air mass are, however, exposed to aging and to contamination, so that the actual air masses that are read differ increasingly over the course of time from the actual air mass. Moreover, fatigue phenomena or the like may induce leakage and other problems in the air intake tract, causing the actually measured air mass to differ from the air mass actually delivered to the internal combustion engine for combustion.